Method of manufacturing crankshaft having weight-reducing forged holes

ABSTRACT

A method of manufacturing a crankshaft having weight-reducing forged holes can achieve lightening and precise forming by additionally including a punching process of using an individual hydraulic press. The method includes steps of: heating a steel bar, performing busting such that the heated steel bar is disposed in a cavity of a mold to be produced as a first intermediate shape of a crankshaft, performing brokering such that the first intermediate shape is produced as a second intermediate shape, performing finishing such that the second intermediate shape is produced as a third intermediate shape, performing trimming such that the third intermediate shape is produced as a complete shape of the crankshaft by cutting portions other than the shape of the crankshaft, and performing punching such that holes are formed in the complete shape of the crankshaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2016-0057762, filed on May 11, 2016 in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

BACKGROUND 1. Field of the Invention

The present invention relates to a method of manufacturing a crankshaft having weight-reducing forged holes, and more particularly, to a method of manufacturing a crankshaft, capable of achieving lightening and precise forming and having improved durability by additionally including a punching process of using an individual hydraulic press.

2. Description of the Related Art

In recent years, improvement in fuel efficiency has become important and antipollution measures have been increasingly enforced in the vehicle industry. Various methods, such as the development of alternative fuels, the improvement of engine efficiency, and design improvements, may be performed in order to improve the fuel efficiency of vehicles and reduce the emission of pollutants such as carbon dioxide. Among them, the most effective method is to reduce the weight of a vehicle. When a vehicle become lighter, the fuel efficiency and acceleration performance thereof are increased, the emission of carbon dioxide is reduced, and the durability of the chassis and tires is improved.

Thus, the lightening of an engine, which is a combination of a large number of parts, is required in order to improve fuel efficiency in a vehicle. The body of the engine includes a crankcase which is equipped with a crankshaft for converting the reciprocating motion of pistons into rotary motion, a cylinder block which has defined therein cylinders in which the pistons reciprocate, and a cylinder head. The parts, such as a piston, a crankshaft, and a connecting rod, moving in each cylinder are referred to as the main moving parts.

The crankshaft is a core part which converts the linear motion transferred from the piston into rotary motion. As engine power and efficiency increase, a larger load is applied to the crankshaft while it rotates. Accordingly, since it is necessary to secure strength and durability in order for the crankshaft to endure the large load, the crankshaft generally must be heavy, among the main moving parts of the engine. Thus, when the size and mass of the crankshaft are reduced, the size and mass of the engine are reduced. Therefore, the crankshaft has a complex influence on the overall size, mass, and fuel efficiency of the vehicle.

The crankshaft, which has a large influence on fuel efficiency, includes a journal shaft part, crankpin parts, arm parts, and counterweight parts. The crankpin parts, which are arranged parallel to the journal shaft part, are connected to the journal shaft part by crank arms, and the counterweight parts are located at the arm parts. The counterweight parts are formed at the opposite sides of the journal shaft part, which is connected with the crankpin parts.

Conventionally, there is a technique for reducing the weight of the crankshaft by forming hollow holes in the crankpin parts of the crankshaft. As such, the forming the holes in the crankpin parts may be suitable since this has a little influence on the strength of the crankshaft.

However, when the holes are formed in the crankpin parts, the holes formed in the respective crankpin parts may differ from each other. In order to reduce variation in quality and a failure rate, it is necessary to perform precise forming by controlling the displacement and the load set in each hydraulic press.

SUMMARY

Thus, in order to resolve the above problems, the present invention has been developed to reduce the weight of a crankshaft and precisely form the crankshaft.

Therefore, it is an object of the present invention to provide a method of manufacturing a crankshaft having weight-reducing forged holes, capable of reducing the weight of a crankshaft, and at the same time, precisely forming the crankshaft in order to reduce variation in quality and a failure rate during the manufacture thereof.

It is another object of the present invention to provide a method of manufacturing a crankshaft having weight-reducing forged holes, capable of allowing the weight of a vehicle engine to be reduced, and allowing a vehicle to have increased durability and reduced weight, thereby increasing fuel efficiency and preventing environmental pollution.

The present invention is not limited to the foregoing objects, and the other objects thereof will be clearly understood by those skilled in the art from the following description.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a method of manufacturing a crankshaft having weight-reducing forged holes, which includes steps of: heating a steel bar; performing busting such that the heated steel bar is disposed in a cavity of a mold including an upper mold and a lower mold to be produced as a first intermediate shape of a crankshaft; performing brokering such that the first intermediate shape is produced as a second intermediate shape; performing finishing such that the second intermediate shape, after the brokering step, is produced as a third intermediate shape; performing trimming such that the third intermediate shape, after the finishing step, is produced as a complete shape of the crankshaft by cutting portions other than the shape of the crankshaft; and performing punching such that holes are formed in the complete shape of the crankshaft after the trimming step.

In the punching step, the holes may be formed in both pin web parts in the complete shape of the crankshaft using hydraulic presses.

The hydraulic presses may be individually applied to the respective pin web parts.

The hydraulic presses may be simultaneously applied to both web parts of one crankpin and both web parts of the other crankpin.

The hydraulic presses may be diagonally applied to both web parts of each of the crankpins.

The holes may be formed in the complete shape of the crankshaft in a state in which the complete shape of the crankshaft, after the trimming step, is heated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 (RELATED ART) is a flowchart illustrating a process of forging a crankshaft according to the related art;

FIG. 2 is a flowchart illustrating a method of manufacturing a crankshaft according to an embodiment of the present invention;

FIG. 3 is a view illustrating a crankshaft manufactured by adding a punching step after a trimming step in the method according to the embodiment of the present invention;

FIG. 4 is a view illustrating the crankshaft manufactured by individually using a hydraulic press for each of the pin web parts thereof in the first and second forming steps of the method according to the embodiment of the present invention;

FIG. 5 is a view illustrating a state in which weight-reducing forged holes are formed in the pin web parts of the crankshaft according to the embodiment of the present invention; and

FIG. 6 is a view illustrating a crankshaft with the weight-reducing forged hole according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, the terms “unit”, “-er”, “-or”, and “module” described in the specification mean units for processing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

Further, the control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).

Hereinafter, the exemplary embodiments of the present invention will be described in detail. The present invention relates to a method of manufacturing a crankshaft having weight-reducing forged holes.

FIG. 1 (RELATED ART) is a flowchart illustrating a process of forging a crankshaft according to the related art. After a steel bar is heated at a temperature of 1200 to 1250° C., the heated steel bar passes through a hot forging process. The hot forging process is classified into a busting step (S11), a brokering step (S13), a finishing step (S15), and a trimming step (S17).

First, the heated steel bar passes through the busting step (S11), in which the heated steel bar is disposed in the cavity of a mold including an upper mold and a lower mold, and is set in a range formable by forging in consideration of the strength and strain of a material so as to correspond to a first intermediate shape. Next, the first intermediate shape is set in a range formable by forging in consideration of the strength and strain of a material, and passes through the brokering step (S13) in which the first intermediate shape is produced as a second intermediate shape. Next, the second intermediate shape, passing through the brokering step (S13), passes through the finishing step (S15) in which the second intermediate shape is produced as a third intermediate shape so as to correspond to the complete shape of the crankshaft. Next, the third intermediate shape, passing through the finishing step (S15), passes through the trimming step (S17) in which portions other than the shape of the crankshaft are cut and the shape of the crankshaft is completed.

FIG. 2 is a flowchart illustrating a method of manufacturing a crankshaft according to an embodiment of the present invention. The method of manufacturing a crankshaft further includes a punching step (S109) such that holes may be formed in the complete shape of the crankshaft after the trimming step. Thereby, the crankshaft having weight-reducing forged holes according to the present invention is finally manufactured.

In more detail, a heated steel bar passes through a busting step (S101) in which the heated steel bar is disposed in the cavity of a mold including an upper mold and a lower mold, and is set in a range formable by forging in consideration of the strength and strain of a material so as to correspond to a first intermediate shape. Next, the first intermediate shape is set in a range formable by forging in consideration of the strength and strain of a material, and passes through a brokering step (S103) in which the first intermediate shape is produced as a second intermediate shape. Next, the second intermediate shape, after the brokering step (S103), passes through a finishing step (S105) in which the second intermediate shape is produced as a third intermediate shape so as to correspond to the complete shape of the crankshaft. Next, the third intermediate shape, after the finishing step (S105), passes through a trimming step (S107) in which portions other than the shape of the crankshaft are cut and the shape of the crankshaft is completed. Next, a punching step (S109) is performed such that holes may be formed in the complete shape of the crankshaft passing through the trimming step (S107). As a result, the crankshaft having weight-reducing forged holes of the present invention is finally manufactured according to the above steps.

FIG. 5 is a view illustrating a state in which the weight-reducing forged holes are formed in the pin web parts of the crankshaft according to the embodiment of the present invention. In particular, each of the pin web parts has a fan shape as a whole, and a weight-reducing forged hole is formed in the upper side of the pin web part, having a relatively small width, rather than the lower side thereof. It may be seen that the hole is formed in the upper side of the pin web part when viewed from the side.

FIG. 3 is a view illustrating the crankshaft manufactured by adding the punching step after the trimming step in the method according to the embodiment of the present invention. In the punching step (S109) of the present invention, the holes are formed in both pin web parts in the complete shape of the crankshaft using hydraulic presses.

The holes must be formed in the complete shape of the crankshaft in the state in which the complete shape of the crankshaft, passing through the punching step (S109) after the trimming step (S107), is heated. In addition, it may be seen that the hydraulic presses are individually used in the respective pin web parts, and are diagonally applied to the pin web parts.

In more detail, FIG. 3 illustrates the crankshaft of a four-cylinder engine having four cylinders. Thus, it may be seen that the crankshaft has four pins. In addition, it may be seen that the pin web parts are located on both sides of each crankpin, and that the total number of pin web parts is eight. The four pins and eight pin web parts are located perpendicular to the axis of the crankshaft.

FIG. 4 is a view illustrating the crankshaft manufactured by individually using the hydraulic press for each of the pin web parts thereof in the first and second forming steps of the method according to the embodiment of the present invention. Similar to that illustrated in FIG. 3, FIG. 4 illustrates that the crankshaft includes the four pins and the eight pin web parts. A first pin 101, a second pin 102, a third pin 103, and a fourth pin 104 are located in this order from left to right in FIG. 4. First and second pin web parts 111 and 112 are located on both sides of the first pin 101, third and fourth pin web parts 113 and 114 are located on both sides of the second pin 102, fifth and sixth pin web parts 115 and 116 are located on both sides of the third pin 103, and seventh and eighth pin web parts 117 and 118 are located on both sides of the fourth pin 104.

The first and second forming steps of the present invention will be described in detail. In the first forming step, holes are formed in the first and second pin web parts 111 and 112 of the first pin 101 and in the fifth and sixth pin web parts 115 and 116 of the third pin 103 using each individual hydraulic press in the mold for punching. In the second forming step after the first forming step, holes are formed in the third and fourth pin web part of the second pin, and in the seventh and eighth pin web parts of the fourth pin using each individual hydraulic press in the mold for punching.

In the first and second forming steps, respective hydraulic presses are simultaneously applied to both web parts of one crankpin and both web parts of the other crankpin.

When the total of two forming steps is performed as described above, the cycle time for forming is not increased compared to that of the related art, but nevertheless, precise forming can be performed owing to the use of individual hydraulic presses. As a result, optimal quality can be achieved.

Accordingly, the crankshaft, which has the holes formed in both pin web parts in the complete shape of the crankshaft using the hydraulic presses, according to the present invention is manufactured through the added punching step (S109) including the first and second forming steps after the trimming step (S107). In this case, individual hydraulic presses are used for the respective pin web parts, and are diagonally applied to the pin web parts. The holes must be formed in the complete shape of the crankshaft in the state in which the complete shape of the crankshaft, passing through the punching step (S109) after the trimming step (S107), is heated.

When the hydraulic presses are individually used for the respective pin web parts, as in the punching step (S109), the crankshaft is controllable by a set displacement and load, and can be precisely formed. Consequently, it is possible to reduce the variation in quality of the crankshaft and the failure rate thereof.

Additionally, FIG. 6 is a view illustrating a crankshaft with the weight-reducing forged hole according to the present invention. The number of holes in the crankshaft according to the related art is 4, whereas the number of holes in the crankshaft according to the present invention is 8 (see FIG. 3). By comparison, when the crankshaft is manufactured, the weight of the crankshaft according to the related art is 9.522 kg, and the weight of the crankshaft according to the present invention is about 9.0 kg.

Accordingly, since the weight of the crankshaft according to the present invention is reduced compared to that of the related art, a significant weight-reducing effect can be expected when the vehicle is manufactured. In addition, it is possible to additionally improve fuel efficiency together with the lightening of the vehicle. Moreover, the manufacturing costs of the crankshaft can be reduced compared to the cutting process of the crankshaft according to the related art, and it is possible to secure good fatigue strength.

In accordance with the method of manufacturing a crankshaft having weight-reducing forged holes of the present invention, it is possible to reduce the weight of the crankshaft, and at the same time, precisely form the crankshaft in order to reduce variation in quality and a failure rate during the manufacture thereof.

In general, the crankshaft is a core part which converts the linear motion transferred from the piston into rotary motion. As engine power and efficiency increase, the crankshaft must rotate while enduring a larger load. Accordingly, it is necessary to increase the strength and durability of the crankshaft. Thus, the crankshaft having weight-reducing forged holes manufactured by the method according to the present invention satisfies all of the above requirements.

In addition, in accordance with the method of manufacturing a crankshaft having weight-reducing forged holes of the present invention, the weight of the vehicle engine can be reduced, and the vehicle can have increased durability and reduced weight, thereby increasing fuel efficiency and preventing environmental pollution.

As is apparent from the above description, in accordance with a method of manufacturing a crankshaft having weight-reducing forged holes of the present invention, it is possible to reduce the weight of a crankshaft, and at the same time, precisely form the crankshaft in order to reduce variation in quality and a failure rate during the manufacture thereof.

In addition, in accordance with the method of manufacturing a crankshaft having weight-reducing forged holes of the present invention, the weight of a vehicle engine can be reduced, and a vehicle can have increased durability and reduced weight, thereby increasing fuel efficiency and preventing environmental pollution.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A method of manufacturing a crankshaft having weight-reducing forged holes, comprising the steps of: heating a steel bar; performing busting such that the heated steel bar is disposed in a cavity of a mold including an upper mold and a lower mold to be produced as a first intermediate shape of a crankshaft; performing brokering such that the first intermediate shape is produced as a second intermediate shape; performing finishing such that the second intermediate shape, after the brokering step, is produced as a third intermediate shape; performing trimming such that the third intermediate shape, after the finishing step, is produced as a complete shape of the crankshaft by cutting portions other than the shape of the crankshaft; and performing punching such that holes are formed in the complete shape of the crankshaft after the trimming step.
 2. The method according to claim 1, wherein, in the punching step, the holes are formed in both pin web parts in the complete shape of the crankshaft using hydraulic presses.
 3. The method according to claim 2, wherein the hydraulic presses are individually applied to the respective pin web parts.
 4. The method according to claim 3, wherein the hydraulic presses are simultaneously applied to both web parts of one crankpin and both web parts of another crankpin.
 5. The method according to claim 4, wherein the hydraulic presses are diagonally applied to both web parts of each of the crankpins.
 6. The method according to claim 1, wherein the holes are formed in the complete shape of the crankshaft in a state in which the complete shape of the crankshaft, after the trimming step, is heated. 